Thrust reversers are well known for shortening the braking distance of an aircraft to increase safety, especially when it is necessary to brake on a damp or icy runway. Typically, a thrust reverser for a jet engine has two or more doors mounted about axes disposed at the downstream end of the engine, proximately at its exhaust. The thrust reverser doors are arranged to pivot from a folded, or stowed, position in which they form part of the nozzle of the engine of the aircraft, to an unfolded, or deployed, position in which they are disposed transversely of the jet output from the aircraft.
Such a thrust reverser can be added to the downstream portion of a number of jet engines, with or without fan by-pass ducts. However, it is believed that the non-planar or "fish-mouth" exit opening provided by stowed reverser doors may affect the efficiency of the engine during its cruising phase, as the effluent exits mouth effect results from the geometrical necessity of the thrust reverser doors having to pivot about respective hinges located at opposite sides, at the downstream portion, of the engine.
When the thrust reverser is installed downstream from the engine, the doors of the reverser, when in the stowed position, form extensions of the ejection nozzle through which the gaseous jet flow passes.
There are various embodiments of these doors which are specifically suited to this type of thrust reverser. For example, it may be advantageous to use the doors described in French Patent FR-A-2 348 371, partially represented in the attached FIG. 11, with the doors in their stowed position. In this case, two doors 102 and 103 of reverser 100 are formed as extensions of a curved wall 104 having a more or less hemitruncated shape, and each of them is stiffened in the area of its longitudinal edges 105 by rectilinear sectional bars 106, and, in the area of its forward arcuate or circular edge (not visible in the Figure) and rear arcuate or circular edge (or trailing edge 107), by arched sectional bars 108, of which the bar for the door 102 is shown in cross-section in FIGS. 11a and 11b. The set of rectilinear and arched sectional bars, 106 and 108 respectively, form a stiffening framework which protrudes in relation to concave surface 110 of each door 102 and 103.
Furthermore, an inner lining 111, attached to wall 104 by means of inclined surfaces 112 and 114, encloses each arched rear sectional bar 108, while within the extension of rear arched sectional bar 108 on each door are arranged two attachment hinges 115, substantially diametrically opposed to each other, which, by means of joints 116, connect doors 102 and 103 to rigid arms 117 emanating from the engine ejection nozzle. Doors 102 and 103 may thus pivot around their downstream transverse hinge pins 118.
As shown in FIG. 11, trailing edges 107 of doors 102 and 103 fall respectively within transverse planes which are inclined symmetrically in relation to the longitudinal axis of the engine, in order to ensure that, when the doors are in the deployed (extended) position (and trailing edges 107 are thus in contact or abut with each other), the direction of the gaseous jet flow is reversed to obtain the desired counter-thrust. Consequently, when the doors are in the stowed (folded) position (FIG. 11), end pieces 107A of the two trailing edges 107, which arise approximately at the level of attachment hinges 115, which form the extension of the ends of the rear arched sectional bars 108, mark off between them two crescent-shaped (or substantially arcuate) indentations 120, and the projections formed from each of these indentations in a lateral plane have an approximately triangular shape forming substantially arcuate notches.
Trailing edge 107 of each door has, in its inclined transverse plane, a varying progressively-increasing thickness, the thickest point of which "E" is found at end pieces 107A close to the joints and matches approximately the height of the rear arched sectional bars 108 (FIGS. 11 and 11b), while the smallest thickness "e" is found in central portion 107B of each trailing edge (FIGS. 11 and 11a).
Consequently, when the section of trailing edges 107 of doors 102 and 103 is projected onto a plane perpendicular to the longitudinal axis of the engine 119, a surface 121, called a base surface by those skilled in the art, is obtained (FIG. 12) which approximately resemble a ring 122 whose thickness "E" at transverse hinge pins 118 of the doors is noticeably greater than the thickness "e" located perpendicularly.
Although the structure of the reverser described in the patent FR-A-2 348 371 and summarized above with reference to FIGS. 11, 11a, 11b and 12, endows the doors with excellent rigidity, while allowing, furthermore, the optimal deflection of the reversed gaseous jet flow, this structure produces additional aerodynamic drag because of the sizable thickness "E" of base surface 121, at trailing edges 107 of the end pieces.
In actuality, when the aircraft is in flight and the doors of the reverser(s) are stowed, small air currents flow along the outer surfaces of the doors and tend to follow the surface of the trailing edges of the doors. Given this phenomenon, and the fact that end pieces 107A of the trailing edges 107 have the thickness "E", which is an important factor in this type of reverser, the air currents would abruptly change direction, thus producing significant aerodynamic turbulence which causes additional drag. The flow of the air currents at the central portions 107B of the trailing edges, meanwhile, is not changed by virtue of the small thickness "e" at these central portions.
To prevent this drag, one solution consists of reducing the thickness "E" of end pieces 107A at the trailing edges.